# frozen_string_literal: true

module Gitlab
  module Ci
    module Interpolation
      ##
      # This class matches the given function string with a predefined
      # function and then applies it to the input value.
      #
      class FunctionsStack
        Output = Struct.new(:value, :errors) do
          def success?
            errors.empty?
          end
        end

        FUNCTIONS = [
          Functions::Truncate
        ].freeze

        attr_reader :errors

        def initialize(function_expressions)
          @errors = []
          @functions = build_stack(function_expressions)
        end

        def valid?
          errors.none?
        end

        def evaluate(input_value)
          return Output.new(nil, errors) unless valid?

          functions.reduce(Output.new(input_value, [])) do |output, function|
            break output unless output.success?

            output_value = function.execute(output.value)

            if function.valid?
              Output.new(output_value, [])
            else
              Output.new(nil, function.errors)
            end
          end
        end

        private

        attr_reader :functions

        def build_stack(function_expressions)
          function_expressions.map do |function_expression|
            matching_function = FUNCTIONS.find { |function| function.matches?(function_expression) }

            if matching_function.present?
              matching_function.new(function_expression)
            else
              message = "no function matching `#{function_expression}`: " \
                        'check that the function name, arguments, and types are correct'

              errors << message
            end
          end
        end
      end
    end
  end
end
